Heart Facts

  • Your heart is the size of your fist. It is inside the middle of your chest, slightly to the left.
  • The heart is a powerful pump made almost entirely of muscle.
  • The heart contracts (tightens) and relaxes automatically about 70 times a minute to pump blood out through your arteries.
  • The heart has two sides separated by a muscle wall called the septum.
  • The right side is smaller and weaker, and it pumps blood only to the lungs.
  • The stronger left side pumps blood around the body.
  • Each side of the heart has two chambers. There is an atrium (plural atria) at the top where blood accumulates (builds up) from the veins, and a ventricle below which contracts to pump blood out into the arteries.
  • Each side of the heart (left and right) ejects about 70 ml of blood every beat.
  • There are two valves in each side of the heart to make sure that blood flows only one way — a large one between the atrium and the ventricle, and a small one at the exit from the ventricle into the artery.
  • The coronary arteries supply the heart. If they become clogged, the heart muscle may be short of blood and stop working. This is what happens in a heart attack.
  • The heartbeat is the regular squeezing of the heart muscle to pump blood around the body.
  • Four heart valves make sure blood only moves one way.
  • The heartbeat is a sequence called the cardiac cycle and it has two phases — systole and diastole.
  • Systole is when the heart muscle contracts (tightens). Diastole is the resting phase between contractions, breathing and blood.
  • Systole begins when a wave of muscle contraction sweeps across the heart and squeezes blood from each of the atria into the two ventricles.
  • When the contraction reaches the ventricles, they squeeze blood out into the arteries.
  • In diastole, the heart muscle relaxes and the atria fill with blood again.
  • Heart muscle on its own would contract automatically.
  • Nerve signals make the heart beat faster or slower.